Silicon is the most common substrate material utilized for integrated circuit fabrication. Accordingly, much of the fabrication process machinery is targeted for use with Silicon. The current state of the art fabrication facilities utilize 200 mm (“8 inch”) to 300 mm (“12 inch”) diameter Silicon wafers. In general, a fabrication facility and a fabrication process are more efficient, e.g., produce more integrated circuits in less time and/or at a lower cost, using a larger wafer size.
A variety of integrated circuit devices benefit from, or require, non-Silicon substrates, for example, light emitting diodes or lasers, optical waveguides, radio-frequency circuits, low power circuitry or radiation hardened circuitry. Wafers grown using materials other than Silicon are generally only available in smaller wafer sizes, for a variety of reasons including crystal growth characteristics, mechanical strength, thermal properties, defect propagation, and the like. For example, such non-Silicon wafers are generally not available in sizes over 100 mm.
One obstacle to the adoption of large, non-Silicon substrates may be the behavior of defects in an epitaxial layer grown on the substrate. Such defects may be caused by a lattice mismatch or a coefficient of thermal expansion (CTE) mismatch between a substrate and an epitaxial layer. When substrate size becomes larger, lattice-mismatch-induced defects propagate along an epitaxial layer, and the amount of thermal-expansion difference is larger. Both of these effects may lead to a deleteriously higher defect ratio and poor production yield when using “large” non-Silicon substrates.